Efficient and effective removal of heat from a system (e.g., circuit, process, etc.) is often of crucial importance for its proper functioning and continued operation.
The need for heat removal arises in a wide variety of technologies and processes across many different industries. Consider, for instance, the electronics industry. It is essential to remove the heat that is generated in digital and analog circuits (e.g., at P−N junctions, at resistors, etc.). The importance of removing heat from the ubiquitous microprocessor, for example, is hard to overestimate. Removing heat from a microprocessor that is part of an integrated circuit is necessary for proper functioning of the microprocessor and the circuit, as well as to support increases in circuit density and operating speed. Furthermore, removing heat from electronic components reduces the internal noise of those components, therefore increasing the sensitivity of devices (e.g., sensors, etc.) that contain them. Also, heat removal can increase circuit/device reliability due to a decrease in thermal stresses.
Heat removal is also important in the chemical and pharmaceutical industries. Many of the systems used in these industries involve exothermic (heat-generating) reactions. Furthermore, biological, medical and related areas dealing with in vivo (i.e., within the body) research and technology applications require heat removal from tissues, cells, biological fluids, and the like. And heat removal is also important for the continued development of the burgeoning “small tech” fields, such as micro-fluidics, MEMS and Nanotechnology. A literally unlimited number of further examples of the importance of heat removal can be found in industries as diverse as the machine tool industry, telecommunications, the military, and food processing industry.
It is relatively inefficient to remove heat by known techniques. This low efficiency (i.e., about 20 to 30 percent) is due, in large part, to an inability to remove heat from the location or “spot in space” at which the heat is actually generated. This problem often arises due to the inaccessibility of the hot spot. As a consequence, heat is often removed over a much larger area, requiring relatively larger cooling elements and a relatively greater amount of energy. Another reason for the relatively low efficiency is the prevalence of thermal exchanges due to conduction and convection.
Various techniques are employed to accelerate the three basic mechanisms of heat exchange, as a function of the specific application. Exemplary techniques include, for convection: forced air, water, heat pipes, etc.; for conduction: heat sinking, Peltier elements, etc.); and for radiation: special coatings and attention to system geometry.
These methods are restricted in their applicability due to energy requirements, size limitations, the incidence of contamination, and other constraints. Especially problematic is the continuing trend toward miniaturization, which presents substantial challenges for known heat removal systems and techniques. Consequently, a need remains for improved cooling techniques that are broadly applicable and easily size-scalable.